[Kaleidoscope][BuildingAJIT] Add code for Chapter 5 - remote JITing.

This chapter demonstrates lazily JITing from ASTs with the expressions being
executed on a remote machine via a TCP connection. It needs some polish, but is
substantially complete.

Currently x86-64 SysV ABI (Darwin and Linux) only, but other architectures
can be supported by changing the server code to use alternative ABI support
classes from llvm/include/llvm/ExecutionEngine/Orc/OrcABISupport.h.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@271193 91177308-0d34-0410-b5e6-96231b3b80d8

7 files changed, 1789 insertions, 0 deletions

diff --git a/examples/Kaleidoscope/BuildingAJIT/CMakeLists.txt b/examples/Kaleidoscope/BuildingAJIT/CMakeLists.txt
index 8315eb6e0e5..17e280c1671 100644
--- a/examples/Kaleidoscope/BuildingAJIT/CMakeLists.txt
+++ b/examples/Kaleidoscope/BuildingAJIT/CMakeLists.txt
@@ -2,4 +2,5 @@ add_subdirectory(Chapter1)
 add_subdirectory(Chapter2)
 add_subdirectory(Chapter3)
 add_subdirectory(Chapter4)
+add_subdirectory(Chapter5)
 
diff --git a/examples/Kaleidoscope/BuildingAJIT/Chapter5/CMakeLists.txt b/examples/Kaleidoscope/BuildingAJIT/Chapter5/CMakeLists.txt
new file mode 100644
index 00000000000..d5b832b4955
--- /dev/null
+++ b/examples/Kaleidoscope/BuildingAJIT/Chapter5/CMakeLists.txt
@@ -0,0 +1,21 @@
+add_subdirectory(Server)
+
+set(LLVM_LINK_COMPONENTS
+  Analysis
+  Core
+  ExecutionEngine
+  InstCombine
+  Object
+  OrcJIT
+  RuntimeDyld
+  ScalarOpts
+  Support
+  TransformUtils
+  native
+  )
+
+add_kaleidoscope_chapter(BuildingAJIT-Ch5
+  toy.cpp
+  )
+
+export_executable_symbols(BuildingAJIT-Ch5)
diff --git a/examples/Kaleidoscope/BuildingAJIT/Chapter5/KaleidoscopeJIT.h b/examples/Kaleidoscope/BuildingAJIT/Chapter5/KaleidoscopeJIT.h
new file mode 100644
index 00000000000..d72dfdde343
--- /dev/null
+++ b/examples/Kaleidoscope/BuildingAJIT/Chapter5/KaleidoscopeJIT.h
@@ -0,0 +1,263 @@
+//===----- KaleidoscopeJIT.h - A simple JIT for Kaleidoscope ----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Contains a simple JIT definition for use in the kaleidoscope tutorials.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_EXECUTIONENGINE_ORC_KALEIDOSCOPEJIT_H
+#define LLVM_EXECUTIONENGINE_ORC_KALEIDOSCOPEJIT_H
+
+#include "RemoteJITUtils.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ExecutionEngine/ExecutionEngine.h"
+#include "llvm/ExecutionEngine/RuntimeDyld.h"
+#include "llvm/ExecutionEngine/SectionMemoryManager.h"
+#include "llvm/ExecutionEngine/Orc/CompileOnDemandLayer.h"
+#include "llvm/ExecutionEngine/Orc/CompileUtils.h"
+#include "llvm/ExecutionEngine/Orc/JITSymbol.h"
+#include "llvm/ExecutionEngine/Orc/IRCompileLayer.h"
+#include "llvm/ExecutionEngine/Orc/IRTransformLayer.h"
+#include "llvm/ExecutionEngine/Orc/LambdaResolver.h"
+#include "llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h"
+#include "llvm/ExecutionEngine/Orc/OrcRemoteTargetClient.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/Mangler.h"
+#include "llvm/Support/DynamicLibrary.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetMachine.h"
+#include <algorithm>
+#include <memory>
+#include <string>
+#include <vector>
+
+class PrototypeAST;
+class ExprAST;
+
+/// FunctionAST - This class represents a function definition itself.
+class FunctionAST {
+  std::unique_ptr<PrototypeAST> Proto;
+  std::unique_ptr<ExprAST> Body;
+
+public:
+  FunctionAST(std::unique_ptr<PrototypeAST> Proto,
+              std::unique_ptr<ExprAST> Body)
+      : Proto(std::move(Proto)), Body(std::move(Body)) {}
+  const PrototypeAST& getProto() const;
+  const std::string& getName() const;
+  llvm::Function *codegen();
+};
+
+/// This will compile FnAST to IR, rename the function to add the given
+/// suffix (needed to prevent a name-clash with the function's stub),
+/// and then take ownership of the module that the function was compiled
+/// into.
+std::unique_ptr<llvm::Module>
+irgenAndTakeOwnership(FunctionAST &FnAST, const std::string &Suffix);
+
+namespace llvm {
+namespace orc {
+
+// Typedef the remote-client API.
+typedef remote::OrcRemoteTargetClient<FDRPCChannel> MyRemote;
+
+class KaleidoscopeJIT {
+private:
+  MyRemote &Remote;
+  std::unique_ptr<TargetMachine> TM;
+  const DataLayout DL;
+  JITCompileCallbackManager *CompileCallbackMgr;
+  std::unique_ptr<IndirectStubsManager> IndirectStubsMgr;
+  ObjectLinkingLayer<> ObjectLayer;
+  IRCompileLayer<decltype(ObjectLayer)> CompileLayer;
+
+  typedef std::function<std::unique_ptr<Module>(std::unique_ptr<Module>)>
+    OptimizeFunction;
+
+  IRTransformLayer<decltype(CompileLayer), OptimizeFunction> OptimizeLayer;
+
+public:
+  typedef decltype(OptimizeLayer)::ModuleSetHandleT ModuleHandle;
+
+  KaleidoscopeJIT(MyRemote &Remote)
+      : Remote(Remote),
+        TM(EngineBuilder().selectTarget()),
+        DL(TM->createDataLayout()),
+        CompileLayer(ObjectLayer, SimpleCompiler(*TM)),
+        OptimizeLayer(CompileLayer,
+                      [this](std::unique_ptr<Module> M) {
+                        return optimizeModule(std::move(M));
+                      }) {
+    auto CCMgrOrErr = Remote.enableCompileCallbacks(0);
+    if (!CCMgrOrErr) {
+      logAllUnhandledErrors(CCMgrOrErr.takeError(), errs(),
+                            "Error enabling remote compile callbacks:");
+      exit(1);
+    }
+    CompileCallbackMgr = &*CCMgrOrErr;
+    std::unique_ptr<MyRemote::RCIndirectStubsManager> ISM;
+    if (auto Err = Remote.createIndirectStubsManager(ISM)) {
+      logAllUnhandledErrors(std::move(Err), errs(),
+                            "Error creating indirect stubs manager:");
+      exit(1);
+    }
+    IndirectStubsMgr = std::move(ISM);
+    llvm::sys::DynamicLibrary::LoadLibraryPermanently(nullptr);
+  }
+
+  TargetMachine &getTargetMachine() { return *TM; }
+
+  ModuleHandle addModule(std::unique_ptr<Module> M) {
+
+    // Build our symbol resolver:
+    // Lambda 1: Look back into the JIT itself to find symbols that are part of
+    //           the same "logical dylib".
+    // Lambda 2: Search for external symbols in the host process.
+    auto Resolver = createLambdaResolver(
+        [&](const std::string &Name) {
+          if (auto Sym = IndirectStubsMgr->findStub(Name, false))
+            return RuntimeDyld::SymbolInfo(Sym.getAddress(), Sym.getFlags());
+          if (auto Sym = OptimizeLayer.findSymbol(Name, false))
+            return RuntimeDyld::SymbolInfo(Sym.getAddress(), Sym.getFlags());
+          return RuntimeDyld::SymbolInfo(nullptr);
+        },
+        [&](const std::string &Name) {
+          if (auto AddrOrErr = Remote.getSymbolAddress(Name))
+            return RuntimeDyld::SymbolInfo(*AddrOrErr,
+                                           JITSymbolFlags::Exported);
+          else {
+            logAllUnhandledErrors(AddrOrErr.takeError(), errs(),
+                                  "Error resolving remote symbol:");
+            exit(1);
+          }
+          return RuntimeDyld::SymbolInfo(nullptr);
+        });
+
+    std::unique_ptr<MyRemote::RCMemoryManager> MemMgr;
+    if (auto Err = Remote.createRemoteMemoryManager(MemMgr)) {
+      logAllUnhandledErrors(std::move(Err), errs(),
+                            "Error creating remote memory manager:");
+      exit(1);
+    }
+
+    // Build a singlton module set to hold our module.
+    std::vector<std::unique_ptr<Module>> Ms;
+    Ms.push_back(std::move(M));
+
+    // Add the set to the JIT with the resolver we created above and a newly
+    // created SectionMemoryManager.
+    return OptimizeLayer.addModuleSet(std::move(Ms),
+                                      std::move(MemMgr),
+                                      std::move(Resolver));
+  }
+
+  Error addFunctionAST(std::unique_ptr<FunctionAST> FnAST) {
+    // Create a CompileCallback - this is the re-entry point into the compiler
+    // for functions that haven't been compiled yet.
+    auto CCInfo = CompileCallbackMgr->getCompileCallback();
+
+    // Create an indirect stub. This serves as the functions "canonical
+    // definition" - an unchanging (constant address) entry point to the
+    // function implementation.
+    // Initially we point the stub's function-pointer at the compile callback
+    // that we just created. In the compile action for the callback (see below)
+    // we will update the stub's function pointer to point at the function
+    // implementation that we just implemented.
+    if (auto Err = IndirectStubsMgr->createStub(mangle(FnAST->getName()),
+                                                CCInfo.getAddress(),
+                                                JITSymbolFlags::Exported))
+      return Err;
+
+    // Move ownership of FnAST to a shared pointer - C++11 lambdas don't support
+    // capture-by-move, which is be required for unique_ptr.
+    auto SharedFnAST = std::shared_ptr<FunctionAST>(std::move(FnAST));
+
+    // Set the action to compile our AST. This lambda will be run if/when
+    // execution hits the compile callback (via the stub).
+    //
+    // The steps to compile are:
+    // (1) IRGen the function.
+    // (2) Add the IR module to the JIT to make it executable like any other
+    //     module.
+    // (3) Use findSymbol to get the address of the compiled function.
+    // (4) Update the stub pointer to point at the implementation so that
+    ///    subsequent calls go directly to it and bypass the compiler.
+    // (5) Return the address of the implementation: this lambda will actually
+    //     be run inside an attempted call to the function, and we need to
+    //     continue on to the implementation to complete the attempted call.
+    //     The JIT runtime (the resolver block) will use the return address of
+    //     this function as the address to continue at once it has reset the
+    //     CPU state to what it was immediately before the call.
+    CCInfo.setCompileAction(
+      [this, SharedFnAST]() {
+        auto M = irgenAndTakeOwnership(*SharedFnAST, "$impl");
+        addModule(std::move(M));
+        auto Sym = findSymbol(SharedFnAST->getName() + "$impl");
+        assert(Sym && "Couldn't find compiled function?");
+        TargetAddress SymAddr = Sym.getAddress();
+        if (auto Err =
+              IndirectStubsMgr->updatePointer(mangle(SharedFnAST->getName()),
+                                              SymAddr)) {
+          logAllUnhandledErrors(std::move(Err), errs(),
+                                "Error updating function pointer: ");
+          exit(1);
+        }
+
+        return SymAddr;
+      });
+
+    return Error::success();
+  }
+
+  Error executeRemoteExpr(TargetAddress ExprAddr) {
+    return Remote.callVoidVoid(ExprAddr);
+  }
+
+  JITSymbol findSymbol(const std::string Name) {
+    return OptimizeLayer.findSymbol(mangle(Name), true);
+  }
+
+  void removeModule(ModuleHandle H) {
+    OptimizeLayer.removeModuleSet(H);
+  }
+
+private:
+
+  std::string mangle(const std::string &Name) {
+    std::string MangledName;
+    raw_string_ostream MangledNameStream(MangledName);
+    Mangler::getNameWithPrefix(MangledNameStream, Name, DL);
+    return MangledNameStream.str();
+  }
+
+  std::unique_ptr<Module> optimizeModule(std::unique_ptr<Module> M) {
+    // Create a function pass manager.
+    auto FPM = llvm::make_unique<legacy::FunctionPassManager>(M.get());
+
+    // Add some optimizations.
+    FPM->add(createInstructionCombiningPass());
+    FPM->add(createReassociatePass());
+    FPM->add(createGVNPass());
+    FPM->add(createCFGSimplificationPass());
+    FPM->doInitialization();
+
+    // Run the optimizations over all functions in the module being added to
+    // the JIT.
+    for (auto &F : *M)
+      FPM->run(F);
+
+    return M;
+  }
+
+};
+
+} // end namespace orc
+} // end namespace llvm
+
+#endif // LLVM_EXECUTIONENGINE_ORC_KALEIDOSCOPEJIT_H
diff --git a/examples/Kaleidoscope/BuildingAJIT/Chapter5/RemoteJITUtils.h b/examples/Kaleidoscope/BuildingAJIT/Chapter5/RemoteJITUtils.h
new file mode 100644
index 00000000000..869d0a7ef39
--- /dev/null
+++ b/examples/Kaleidoscope/BuildingAJIT/Chapter5/RemoteJITUtils.h
@@ -0,0 +1,74 @@
+//===-- RemoteJITUtils.h - Utilities for remote-JITing with LLI -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Utilities for remote-JITing with LLI.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TOOLS_LLI_REMOTEJITUTILS_H
+#define LLVM_TOOLS_LLI_REMOTEJITUTILS_H
+
+#include "llvm/ExecutionEngine/Orc/RPCChannel.h"
+#include "llvm/ExecutionEngine/RTDyldMemoryManager.h"
+#include <mutex>
+
+#if !defined(_MSC_VER) && !defined(__MINGW32__)
+#include <unistd.h>
+#else
+#include <io.h>
+#endif
+
+/// RPC channel that reads from and writes from file descriptors.
+class FDRPCChannel final : public llvm::orc::remote::RPCChannel {
+public:
+  FDRPCChannel(int InFD, int OutFD) : InFD(InFD), OutFD(OutFD) {}
+
+  llvm::Error readBytes(char *Dst, unsigned Size) override {
+    assert(Dst && "Attempt to read into null.");
+    ssize_t Completed = 0;
+    while (Completed < static_cast<ssize_t>(Size)) {
+      ssize_t Read = ::read(InFD, Dst + Completed, Size - Completed);
+      if (Read <= 0) {
+        auto ErrNo = errno;
+        if (ErrNo == EAGAIN || ErrNo == EINTR)
+          continue;
+        else
+          return llvm::errorCodeToError(
+                   std::error_code(errno, std::generic_category()));
+      }
+      Completed += Read;
+    }
+    return llvm::Error::success();
+  }
+
+  llvm::Error appendBytes(const char *Src, unsigned Size) override {
+    assert(Src && "Attempt to append from null.");
+    ssize_t Completed = 0;
+    while (Completed < static_cast<ssize_t>(Size)) {
+      ssize_t Written = ::write(OutFD, Src + Completed, Size - Completed);
+      if (Written < 0) {
+        auto ErrNo = errno;
+        if (ErrNo == EAGAIN || ErrNo == EINTR)
+          continue;
+        else
+          return llvm::errorCodeToError(
+                   std::error_code(errno, std::generic_category()));
+      }
+      Completed += Written;
+    }
+    return llvm::Error::success();
+  }
+
+  llvm::Error send() override { return llvm::Error::success(); }
+
+private:
+  int InFD, OutFD;
+};
+
+#endif
diff --git a/examples/Kaleidoscope/BuildingAJIT/Chapter5/Server/CMakeLists.txt b/examples/Kaleidoscope/BuildingAJIT/Chapter5/Server/CMakeLists.txt
new file mode 100644
index 00000000000..15dd53516ce
--- /dev/null
+++ b/examples/Kaleidoscope/BuildingAJIT/Chapter5/Server/CMakeLists.txt
@@ -0,0 +1,17 @@
+set(LLVM_LINK_COMPONENTS
+  Analysis
+  Core
+  ExecutionEngine
+  InstCombine
+  Object
+  OrcJIT
+  RuntimeDyld
+  ScalarOpts
+  Support
+  TransformUtils
+  native
+  )
+
+add_kaleidoscope_chapter(BuildingAJIT-Ch5-Server
+  server.cpp
+  )
diff --git a/examples/Kaleidoscope/BuildingAJIT/Chapter5/Server/server.cpp b/examples/Kaleidoscope/BuildingAJIT/Chapter5/Server/server.cpp
new file mode 100644
index 00000000000..c53e22fe83a
--- /dev/null
+++ b/examples/Kaleidoscope/BuildingAJIT/Chapter5/Server/server.cpp
@@ -0,0 +1,119 @@
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/DynamicLibrary.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/ExecutionEngine/Orc/OrcRemoteTargetServer.h"
+#include "llvm/ExecutionEngine/Orc/OrcABISupport.h"
+
+#include "../RemoteJITUtils.h"
+
+#include <cstring>
+#include <unistd.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+
+
+using namespace llvm;
+using namespace llvm::orc;
+
+// Command line argument for TCP port.
+cl::opt<uint32_t> Port("port",
+                       cl::desc("TCP port to listen on"),
+                       cl::init(20000));
+
+ExitOnError ExitOnErr;
+
+typedef int (*MainFun)(int, const char*[]);
+
+template <typename NativePtrT>
+NativePtrT MakeNative(uint64_t P) {
+  return reinterpret_cast<NativePtrT>(static_cast<uintptr_t>(P));
+}
+
+extern "C"
+void printExprResult(double Val) {
+  printf("Expression evaluated to: %f\n", Val);
+}
+
+// --- LAZY COMPILE TEST ---
+int main(int argc, char* argv[]) {
+
+  if (argc == 0)
+    ExitOnErr.setBanner("jit_server: ");
+  else
+    ExitOnErr.setBanner(std::string(argv[0]) + ": ");
+
+  // --- Initialize LLVM ---
+  cl::ParseCommandLineOptions(argc, argv, "LLVM lazy JIT example.\n");
+
+  InitializeNativeTarget();
+  InitializeNativeTargetAsmPrinter();
+  InitializeNativeTargetAsmParser();
+
+  if (sys::DynamicLibrary::LoadLibraryPermanently(nullptr)) {
+    errs() << "Error loading program symbols.\n";
+    return 1;
+  }
+
+  // --- Initialize remote connection ---
+
+  int sockfd = socket(PF_INET, SOCK_STREAM, 0);
+  sockaddr_in servAddr, clientAddr;
+  socklen_t clientAddrLen = sizeof(clientAddr);
+  bzero(&servAddr, sizeof(servAddr));
+  servAddr.sin_family = PF_INET;
+  servAddr.sin_family = INADDR_ANY;
+  servAddr.sin_port = htons(Port);
+
+  {
+    // avoid "Address already in use" error.
+    int yes=1;
+    if (setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
+      errs() << "Error calling setsockopt.\n";
+      return 1;
+    }
+  }
+
+  if (bind(sockfd, reinterpret_cast<sockaddr*>(&servAddr),
+           sizeof(servAddr)) < 0) {
+    errs() << "Error on binding.\n";
+    return 1;
+  }
+  listen(sockfd, 1);
+  int newsockfd = accept(sockfd, reinterpret_cast<sockaddr*>(&clientAddr),
+                         &clientAddrLen);
+
+  auto SymbolLookup =
+    [](const std::string &Name) {
+      return RTDyldMemoryManager::getSymbolAddressInProcess(Name);
+    };
+
+  auto RegisterEHFrames =
+    [](uint8_t *Addr, uint32_t Size) {
+      RTDyldMemoryManager::registerEHFramesInProcess(Addr, Size);
+    };
+
+  auto DeregisterEHFrames =
+    [](uint8_t *Addr, uint32_t Size) {
+      RTDyldMemoryManager::deregisterEHFramesInProcess(Addr, Size);
+    };
+
+  FDRPCChannel TCPChannel(newsockfd, newsockfd);
+  typedef remote::OrcRemoteTargetServer<FDRPCChannel, OrcX86_64_SysV> MyServerT;
+
+  MyServerT Server(TCPChannel, SymbolLookup, RegisterEHFrames, DeregisterEHFrames);
+
+  while (1) {
+    MyServerT::JITFuncId Id = MyServerT::InvalidId;
+    ExitOnErr(Server.startReceivingFunction(TCPChannel, (uint32_t&)Id));
+    switch (Id) {
+    case MyServerT::TerminateSessionId:
+      ExitOnErr(Server.handleTerminateSession());
+      return 0;
+    default:
+      ExitOnErr(Server.handleKnownFunction(Id));
+      break;
+    }
+  }
+
+  llvm_unreachable("Fell through server command loop.");
+}
diff --git a/examples/Kaleidoscope/BuildingAJIT/Chapter5/toy.cpp b/examples/Kaleidoscope/BuildingAJIT/Chapter5/toy.cpp
new file mode 100644
index 00000000000..9c21098971a
--- /dev/null
+++ b/examples/Kaleidoscope/BuildingAJIT/Chapter5/toy.cpp
@@ -0,0 +1,1294 @@
+#include "llvm/ADT/APFloat.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/Verifier.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Scalar/GVN.h"
+#include "KaleidoscopeJIT.h"
+#include <cassert>
+#include <cctype>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <map>
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include <netdb.h>
+#include <unistd.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+
+using namespace llvm;
+using namespace llvm::orc;
+
+// Command line argument for TCP hostname.
+cl::opt<std::string> HostName("hostname",
+                              cl::desc("TCP hostname to connect to"),
+                              cl::init("localhost"));
+
+// Command line argument for TCP port.
+cl::opt<uint32_t> Port("port",
+                       cl::desc("TCP port to connect to"),
+                       cl::init(20000));
+
+//===----------------------------------------------------------------------===//
+// Lexer
+//===----------------------------------------------------------------------===//
+
+// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
+// of these for known things.
+enum Token {
+  tok_eof = -1,
+
+  // commands
+  tok_def = -2,
+  tok_extern = -3,
+
+  // primary
+  tok_identifier = -4,
+  tok_number = -5,
+
+  // control
+  tok_if = -6,
+  tok_then = -7,
+  tok_else = -8,
+  tok_for = -9,
+  tok_in = -10,
+
+  // operators
+  tok_binary = -11,
+  tok_unary = -12,
+
+  // var definition
+  tok_var = -13
+};
+
+static std::string IdentifierStr; // Filled in if tok_identifier
+static double NumVal;             // Filled in if tok_number
+
+/// gettok - Return the next token from standard input.
+static int gettok() {
+  static int LastChar = ' ';
+
+  // Skip any whitespace.
+  while (isspace(LastChar))
+    LastChar = getchar();
+
+  if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
+    IdentifierStr = LastChar;
+    while (isalnum((LastChar = getchar())))
+      IdentifierStr += LastChar;
+
+    if (IdentifierStr == "def")
+      return tok_def;
+    if (IdentifierStr == "extern")
+      return tok_extern;
+    if (IdentifierStr == "if")
+      return tok_if;
+    if (IdentifierStr == "then")
+      return tok_then;
+    if (IdentifierStr == "else")
+      return tok_else;
+    if (IdentifierStr == "for")
+      return tok_for;
+    if (IdentifierStr == "in")
+      return tok_in;
+    if (IdentifierStr == "binary")
+      return tok_binary;
+    if (IdentifierStr == "unary")
+      return tok_unary;
+    if (IdentifierStr == "var")
+      return tok_var;
+    return tok_identifier;
+  }
+
+  if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
+    std::string NumStr;
+    do {
+      NumStr += LastChar;
+      LastChar = getchar();
+    } while (isdigit(LastChar) || LastChar == '.');
+
+    NumVal = strtod(NumStr.c_str(), nullptr);
+    return tok_number;
+  }
+
+  if (LastChar == '#') {
+    // Comment until end of line.
+    do
+      LastChar = getchar();
+    while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
+
+    if (LastChar != EOF)
+      return gettok();
+  }
+
+  // Check for end of file.  Don't eat the EOF.
+  if (LastChar == EOF)
+    return tok_eof;
+
+  // Otherwise, just return the character as its ascii value.
+  int ThisChar = LastChar;
+  LastChar = getchar();
+  return ThisChar;
+}
+
+//===----------------------------------------------------------------------===//
+// Abstract Syntax Tree (aka Parse Tree)
+//===----------------------------------------------------------------------===//
+
+/// ExprAST - Base class for all expression nodes.
+class ExprAST {
+public:
+  virtual ~ExprAST() {}
+  virtual Value *codegen() = 0;
+};
+
+/// NumberExprAST - Expression class for numeric literals like "1.0".
+class NumberExprAST : public ExprAST {
+  double Val;
+
+public:
+  NumberExprAST(double Val) : Val(Val) {}
+  Value *codegen() override;
+};
+
+/// VariableExprAST - Expression class for referencing a variable, like "a".
+class VariableExprAST : public ExprAST {
+  std::string Name;
+
+public:
+  VariableExprAST(const std::string &Name) : Name(Name) {}
+  const std::string &getName() const { return Name; }
+  Value *codegen() override;
+};
+
+/// UnaryExprAST - Expression class for a unary operator.
+class UnaryExprAST : public ExprAST {
+  char Opcode;
+  std::unique_ptr<ExprAST> Operand;
+
+public:
+  UnaryExprAST(char Opcode, std::unique_ptr<ExprAST> Operand)
+      : Opcode(Opcode), Operand(std::move(Operand)) {}
+  Value *codegen() override;
+};
+
+/// BinaryExprAST - Expression class for a binary operator.
+class BinaryExprAST : public ExprAST {
+  char Op;
+  std::unique_ptr<ExprAST> LHS, RHS;
+
+public:
+  BinaryExprAST(char Op, std::unique_ptr<ExprAST> LHS,
+                std::unique_ptr<ExprAST> RHS)
+      : Op(Op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
+  Value *codegen() override;
+};
+
+/// CallExprAST - Expression class for function calls.
+class CallExprAST : public ExprAST {
+  std::string Callee;
+  std::vector<std::unique_ptr<ExprAST>> Args;
+
+public:
+  CallExprAST(const std::string &Callee,
+              std::vector<std::unique_ptr<ExprAST>> Args)
+      : Callee(Callee), Args(std::move(Args)) {}
+  Value *codegen() override;
+};
+
+/// IfExprAST - Expression class for if/then/else.
+class IfExprAST : public ExprAST {
+  std::unique_ptr<ExprAST> Cond, Then, Else;
+
+public:
+  IfExprAST(std::unique_ptr<ExprAST> Cond, std::unique_ptr<ExprAST> Then,
+            std::unique_ptr<ExprAST> Else)
+      : Cond(std::move(Cond)), Then(std::move(Then)), Else(std::move(Else)) {}
+  Value *codegen() override;
+};
+
+/// ForExprAST - Expression class for for/in.
+class ForExprAST : public ExprAST {
+  std::string VarName;
+  std::unique_ptr<ExprAST> Start, End, Step, Body;
+
+public:
+  ForExprAST(const std::string &VarName, std::unique_ptr<ExprAST> Start,
+             std::unique_ptr<ExprAST> End, std::unique_ptr<ExprAST> Step,
+             std::unique_ptr<ExprAST> Body)
+      : VarName(VarName), Start(std::move(Start)), End(std::move(End)),
+        Step(std::move(Step)), Body(std::move(Body)) {}
+  Value *codegen() override;
+};
+
+/// VarExprAST - Expression class for var/in
+class VarExprAST : public ExprAST {
+  std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+  std::unique_ptr<ExprAST> Body;
+
+public:
+  VarExprAST(
+      std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames,
+      std::unique_ptr<ExprAST> Body)
+      : VarNames(std::move(VarNames)), Body(std::move(Body)) {}
+  Value *codegen() override;
+};
+
+/// PrototypeAST - This class represents the "prototype" for a function,
+/// which captures its name, and its argument names (thus implicitly the number
+/// of arguments the function takes), as well as if it is an operator.
+class PrototypeAST {
+  std::string Name;
+  std::vector<std::string> Args;
+  bool IsOperator;
+  unsigned Precedence; // Precedence if a binary op.
+
+public:
+  PrototypeAST(const std::string &Name, std::vector<std::string> Args,
+               bool IsOperator = false, unsigned Prec = 0)
+      : Name(Name), Args(std::move(Args)), IsOperator(IsOperator),
+        Precedence(Prec) {}
+  Function *codegen();
+  const std::string &getName() const { return Name; }
+
+  bool isUnaryOp() const { return IsOperator && Args.size() == 1; }
+  bool isBinaryOp() const { return IsOperator && Args.size() == 2; }
+
+  char getOperatorName() const {
+    assert(isUnaryOp() || isBinaryOp());
+    return Name[Name.size() - 1];
+  }
+
+  unsigned getBinaryPrecedence() const { return Precedence; }
+};
+
+//===----------------------------------------------------------------------===//
+// Parser
+//===----------------------------------------------------------------------===//
+
+/// CurTok/getNextToken - Provide a simple token buffer.  CurTok is the current
+/// token the parser is looking at.  getNextToken reads another token from the
+/// lexer and updates CurTok with its results.
+static int CurTok;
+static int getNextToken() { return CurTok = gettok(); }
+
+/// BinopPrecedence - This holds the precedence for each binary operator that is
+/// defined.
+static std::map<char, int> BinopPrecedence;
+
+/// GetTokPrecedence - Get the precedence of the pending binary operator token.
+static int GetTokPrecedence() {
+  if (!isascii(CurTok))
+    return -1;
+
+  // Make sure it's a declared binop.
+  int TokPrec = BinopPrecedence[CurTok];
+  if (TokPrec <= 0)
+    return -1;
+  return TokPrec;
+}
+
+/// LogError* - These are little helper functions for error handling.
+std::unique_ptr<ExprAST> LogError(const char *Str) {
+  fprintf(stderr, "Error: %s\n", Str);
+  return nullptr;
+}
+
+std::unique_ptr<PrototypeAST> LogErrorP(const char *Str) {
+  LogError(Str);
+  return nullptr;
+}
+
+static std::unique_ptr<ExprAST> ParseExpression();
+
+/// numberexpr ::= number
+static std::unique_ptr<ExprAST> ParseNumberExpr() {
+  auto Result = llvm::make_unique<NumberExprAST>(NumVal);
+  getNextToken(); // consume the number
+  return std::move(Result);
+}
+
+/// parenexpr ::= '(' expression ')'
+static std::unique_ptr<ExprAST> ParseParenExpr() {
+  getNextToken(); // eat (.
+  auto V = ParseExpression();
+  if (!V)
+    return nullptr;
+
+  if (CurTok != ')')
+    return LogError("expected ')'");
+  getNextToken(); // eat ).
+  return V;
+}
+
+/// identifierexpr
+///   ::= identifier
+///   ::= identifier '(' expression* ')'
+static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
+  std::string IdName = IdentifierStr;
+
+  getNextToken(); // eat identifier.
+
+  if (CurTok != '(') // Simple variable ref.
+    return llvm::make_unique<VariableExprAST>(IdName);
+
+  // Call.
+  getNextToken(); // eat (
+  std::vector<std::unique_ptr<ExprAST>> Args;
+  if (CurTok != ')') {
+    while (true) {
+      if (auto Arg = ParseExpression())
+        Args.push_back(std::move(Arg));
+      else
+        return nullptr;
+
+      if (CurTok == ')')
+        break;
+
+      if (CurTok != ',')
+        return LogError("Expected ')' or ',' in argument list");
+      getNextToken();
+    }
+  }
+
+  // Eat the ')'.
+  getNextToken();
+
+  return llvm::make_unique<CallExprAST>(IdName, std::move(Args));
+}
+
+/// ifexpr ::= 'if' expression 'then' expression 'else' expression
+static std::unique_ptr<ExprAST> ParseIfExpr() {
+  getNextToken(); // eat the if.
+
+  // condition.
+  auto Cond = ParseExpression();
+  if (!Cond)
+    return nullptr;
+
+  if (CurTok != tok_then)
+    return LogError("expected then");
+  getNextToken(); // eat the then
+
+  auto Then = ParseExpression();
+  if (!Then)
+    return nullptr;
+
+  if (CurTok != tok_else)
+    return LogError("expected else");
+
+  getNextToken();
+
+  auto Else = ParseExpression();
+  if (!Else)
+    return nullptr;
+
+  return llvm::make_unique<IfExprAST>(std::move(Cond), std::move(Then),
+                                      std::move(Else));
+}
+
+/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
+static std::unique_ptr<ExprAST> ParseForExpr() {
+  getNextToken(); // eat the for.
+
+  if (CurTok != tok_identifier)
+    return LogError("expected identifier after for");
+
+  std::string IdName = IdentifierStr;
+  getNextToken(); // eat identifier.
+
+  if (CurTok != '=')
+    return LogError("expected '=' after for");
+  getNextToken(); // eat '='.
+
+  auto Start = ParseExpression();
+  if (!Start)
+    return nullptr;
+  if (CurTok != ',')
+    return LogError("expected ',' after for start value");
+  getNextToken();
+
+  auto End = ParseExpression();
+  if (!End)
+    return nullptr;
+
+  // The step value is optional.
+  std::unique_ptr<ExprAST> Step;
+  if (CurTok == ',') {
+    getNextToken();
+    Step = ParseExpression();
+    if (!Step)
+      return nullptr;
+  }
+
+  if (CurTok != tok_in)
+    return LogError("expected 'in' after for");
+  getNextToken(); // eat 'in'.
+
+  auto Body = ParseExpression();
+  if (!Body)
+    return nullptr;
+
+  return llvm::make_unique<ForExprAST>(IdName, std::move(Start), std::move(End),
+                                       std::move(Step), std::move(Body));
+}
+
+/// varexpr ::= 'var' identifier ('=' expression)?
+//                    (',' identifier ('=' expression)?)* 'in' expression
+static std::unique_ptr<ExprAST> ParseVarExpr() {
+  getNextToken(); // eat the var.
+
+  std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
+
+  // At least one variable name is required.
+  if (CurTok != tok_identifier)
+    return LogError("expected identifier after var");
+
+  while (true) {
+    std::string Name = IdentifierStr;
+    getNextToken(); // eat identifier.
+
+    // Read the optional initializer.
+    std::unique_ptr<ExprAST> Init = nullptr;
+    if (CurTok == '=') {
+      getNextToken(); // eat the '='.
+
+      Init = ParseExpression();
+      if (!Init)
+        return nullptr;
+    }
+
+    VarNames.push_back(std::make_pair(Name, std::move(Init)));
+
+    // End of var list, exit loop.
+    if (CurTok != ',')
+      break;
+    getNextToken(); // eat the ','.
+
+    if (CurTok != tok_identifier)
+      return LogError("expected identifier list after var");
+  }
+
+  // At this point, we have to have 'in'.
+  if (CurTok != tok_in)
+    return LogError("expected 'in' keyword after 'var'");
+  getNextToken(); // eat 'in'.
+
+  auto Body = ParseExpression();
+  if (!Body)
+    return nullptr;
+
+  return llvm::make_unique<VarExprAST>(std::move(VarNames), std::move(Body));
+}
+
+/// primary
+///   ::= identifierexpr
+///   ::= numberexpr
+///   ::= parenexpr
+///   ::= ifexpr
+///   ::= forexpr
+///   ::= varexpr
+static std::unique_ptr<ExprAST> ParsePrimary() {
+  switch (CurTok) {
+  default:
+    return LogError("unknown token when expecting an expression");
+  case tok_identifier:
+    return ParseIdentifierExpr();
+  case tok_number:
+    return ParseNumberExpr();
+  case '(':
+    return ParseParenExpr();
+  case tok_if:
+    return ParseIfExpr();
+  case tok_for:
+    return ParseForExpr();
+  case tok_var:
+    return ParseVarExpr();
+  }
+}
+
+/// unary
+///   ::= primary
+///   ::= '!' unary
+static std::unique_ptr<ExprAST> ParseUnary() {
+  // If the current token is not an operator, it must be a primary expr.
+  if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
+    return ParsePrimary();
+
+  // If this is a unary operator, read it.
+  int Opc = CurTok;
+  getNextToken();
+  if (auto Operand = ParseUnary())
+    return llvm::make_unique<UnaryExprAST>(Opc, std::move(Operand));
+  return nullptr;
+}
+
+/// binoprhs
+///   ::= ('+' unary)*
+static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
+                                              std::unique_ptr<ExprAST> LHS) {
+  // If this is a binop, find its precedence.
+  while (true) {
+    int TokPrec = GetTokPrecedence();
+
+    // If this is a binop that binds at least as tightly as the current binop,
+    // consume it, otherwise we are done.
+    if (TokPrec < ExprPrec)
+      return LHS;
+
+    // Okay, we know this is a binop.
+    int BinOp = CurTok;
+    getNextToken(); // eat binop
+
+    // Parse the unary expression after the binary operator.
+    auto RHS = ParseUnary();
+    if (!RHS)
+      return nullptr;
+
+    // If BinOp binds less tightly with RHS than the operator after RHS, let
+    // the pending operator take RHS as its LHS.
+    int NextPrec = GetTokPrecedence();
+    if (TokPrec < NextPrec) {
+      RHS = ParseBinOpRHS(TokPrec + 1, std::move(RHS));
+      if (!RHS)
+        return nullptr;
+    }
+
+    // Merge LHS/RHS.
+    LHS =
+        llvm::make_unique<BinaryExprAST>(BinOp, std::move(LHS), std::move(RHS));
+  }
+}
+
+/// expression
+///   ::= unary binoprhs
+///
+static std::unique_ptr<ExprAST> ParseExpression() {
+  auto LHS = ParseUnary();
+  if (!LHS)
+    return nullptr;
+
+  return ParseBinOpRHS(0, std::move(LHS));
+}
+
+/// prototype
+///   ::= id '(' id* ')'
+///   ::= binary LETTER number? (id, id)
+///   ::= unary LETTER (id)
+static std::unique_ptr<PrototypeAST> ParsePrototype() {
+  std::string FnName;
+
+  unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
+  unsigned BinaryPrecedence = 30;
+
+  switch (CurTok) {
+  default:
+    return LogErrorP("Expected function name in prototype");
+  case tok_identifier:
+    FnName = IdentifierStr;
+    Kind = 0;
+    getNextToken();
+    break;
+  case tok_unary:
+    getNextToken();
+    if (!isascii(CurTok))
+      return LogErrorP("Expected unary operator");
+    FnName = "unary";
+    FnName += (char)CurTok;
+    Kind = 1;
+    getNextToken();
+    break;
+  case tok_binary:
+    getNextToken();
+    if (!isascii(CurTok))
+      return LogErrorP("Expected binary operator");
+    FnName = "binary";
+    FnName += (char)CurTok;
+    Kind = 2;
+    getNextToken();
+
+    // Read the precedence if present.
+    if (CurTok == tok_number) {
+      if (NumVal < 1 || NumVal > 100)
+        return LogErrorP("Invalid precedecnce: must be 1..100");
+      BinaryPrecedence = (unsigned)NumVal;
+      getNextToken();
+    }
+    break;
+  }
+
+  if (CurTok != '(')
+    return LogErrorP("Expected '(' in prototype");
+
+  std::vector<std::string> ArgNames;
+  while (getNextToken() == tok_identifier)
+    ArgNames.push_back(IdentifierStr);
+  if (CurTok != ')')
+    return LogErrorP("Expected ')' in prototype");
+
+  // success.
+  getNextToken(); // eat ')'.
+
+  // Verify right number of names for operator.
+  if (Kind && ArgNames.size() != Kind)
+    return LogErrorP("Invalid number of operands for operator");
+
+  return llvm::make_unique<PrototypeAST>(FnName, ArgNames, Kind != 0,
+                                         BinaryPrecedence);
+}
+
+/// definition ::= 'def' prototype expression
+static std::unique_ptr<FunctionAST> ParseDefinition() {
+  getNextToken(); // eat def.
+  auto Proto = ParsePrototype();
+  if (!Proto)
+    return nullptr;
+
+  if (auto E = ParseExpression())
+    return llvm::make_unique<FunctionAST>(std::move(Proto), std::move(E));
+  return nullptr;
+}
+
+/// toplevelexpr ::= expression
+static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
+  if (auto E = ParseExpression()) {
+
+    auto PEArgs = std::vector<std::unique_ptr<ExprAST>>();
+    PEArgs.push_back(std::move(E));
+    auto PrintExpr =
+      llvm::make_unique<CallExprAST>("printExprResult", std::move(PEArgs));
+
+    // Make an anonymous proto.
+    auto Proto = llvm::make_unique<PrototypeAST>("__anon_expr",
+                                                 std::vector<std::string>());
+    return llvm::make_unique<FunctionAST>(std::move(Proto),
+                                          std::move(PrintExpr));
+  }
+  return nullptr;
+}
+
+/// external ::= 'extern' prototype
+static std::unique_ptr<PrototypeAST> ParseExtern() {
+  getNextToken(); // eat extern.
+  return ParsePrototype();
+}
+
+//===----------------------------------------------------------------------===//
+// Code Generation
+//===----------------------------------------------------------------------===//
+
+static LLVMContext TheContext;
+static IRBuilder<> Builder(TheContext);
+static std::unique_ptr<Module> TheModule;
+static std::map<std::string, AllocaInst *> NamedValues;
+static std::unique_ptr<KaleidoscopeJIT> TheJIT;
+static std::map<std::string, std::unique_ptr<PrototypeAST>> FunctionProtos;
+static ExitOnError ExitOnErr;
+
+Value *LogErrorV(const char *Str) {
+  LogError(Str);
+  return nullptr;
+}
+
+Function *getFunction(std::string Name) {
+  // First, see if the function has already been added to the current module.
+  if (auto *F = TheModule->getFunction(Name))
+    return F;
+
+  // If not, check whether we can codegen the declaration from some existing
+  // prototype.
+  auto FI = FunctionProtos.find(Name);
+  if (FI != FunctionProtos.end())
+    return FI->second->codegen();
+
+  // If no existing prototype exists, return null.
+  return nullptr;
+}
+
+/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
+/// the function.  This is used for mutable variables etc.
+static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
+                                          const std::string &VarName) {
+  IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
+                   TheFunction->getEntryBlock().begin());
+  return TmpB.CreateAlloca(Type::getDoubleTy(TheContext), nullptr, VarName);
+}
+
+Value *NumberExprAST::codegen() {
+  return ConstantFP::get(TheContext, APFloat(Val));
+}
+
+Value *VariableExprAST::codegen() {
+  // Look this variable up in the function.
+  Value *V = NamedValues[Name];
+  if (!V)
+    return LogErrorV("Unknown variable name");
+
+  // Load the value.
+  return Builder.CreateLoad(V, Name.c_str());
+}
+
+Value *UnaryExprAST::codegen() {
+  Value *OperandV = Operand->codegen();
+  if (!OperandV)
+    return nullptr;
+
+  Function *F = getFunction(std::string("unary") + Opcode);
+  if (!F)
+    return LogErrorV("Unknown unary operator");
+
+  return Builder.CreateCall(F, OperandV, "unop");
+}
+
+Value *BinaryExprAST::codegen() {
+  // Special case '=' because we don't want to emit the LHS as an expression.
+  if (Op == '=') {
+    // Assignment requires the LHS to be an identifier.
+    // This assume we're building without RTTI because LLVM builds that way by
+    // default.  If you build LLVM with RTTI this can be changed to a
+    // dynamic_cast for automatic error checking.
+    VariableExprAST *LHSE = static_cast<VariableExprAST *>(LHS.get());
+    if (!LHSE)
+      return LogErrorV("destination of '=' must be a variable");
+    // Codegen the RHS.
+    Value *Val = RHS->codegen();
+    if (!Val)
+      return nullptr;
+
+    // Look up the name.
+    Value *Variable = NamedValues[LHSE->getName()];
+    if (!Variable)
+      return LogErrorV("Unknown variable name");
+
+    Builder.CreateStore(Val, Variable);
+    return Val;
+  }
+
+  Value *L = LHS->codegen();
+  Value *R = RHS->codegen();
+  if (!L || !R)
+    return nullptr;
+
+  switch (Op) {
+  case '+':
+    return Builder.CreateFAdd(L, R, "addtmp");
+  case '-':
+    return Builder.CreateFSub(L, R, "subtmp");
+  case '*':
+    return Builder.CreateFMul(L, R, "multmp");
+  case '<':
+    L = Builder.CreateFCmpULT(L, R, "cmptmp");
+    // Convert bool 0/1 to double 0.0 or 1.0
+    return Builder.CreateUIToFP(L, Type::getDoubleTy(TheContext), "booltmp");
+  default:
+    break;
+  }
+
+  // If it wasn't a builtin binary operator, it must be a user defined one. Emit
+  // a call to it.
+  Function *F = getFunction(std::string("binary") + Op);
+  assert(F && "binary operator not found!");
+
+  Value *Ops[] = {L, R};
+  return Builder.CreateCall(F, Ops, "binop");
+}
+
+Value *CallExprAST::codegen() {
+  // Look up the name in the global module table.
+  Function *CalleeF = getFunction(Callee);
+  if (!CalleeF)
+    return LogErrorV("Unknown function referenced");
+
+  // If argument mismatch error.
+  if (CalleeF->arg_size() != Args.size())
+    return LogErrorV("Incorrect # arguments passed");
+
+  std::vector<Value *> ArgsV;
+  for (unsigned i = 0, e = Args.size(); i != e; ++i) {
+    ArgsV.push_back(Args[i]->codegen());
+    if (!ArgsV.back())
+      return nullptr;
+  }
+
+  return Builder.CreateCall(CalleeF, ArgsV, "calltmp");
+}
+
+Value *IfExprAST::codegen() {
+  Value *CondV = Cond->codegen();
+  if (!CondV)
+    return nullptr;
+
+  // Convert condition to a bool by comparing equal to 0.0.
+  CondV = Builder.CreateFCmpONE(
+      CondV, ConstantFP::get(TheContext, APFloat(0.0)), "ifcond");
+
+  Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+  // Create blocks for the then and else cases.  Insert the 'then' block at the
+  // end of the function.
+  BasicBlock *ThenBB = BasicBlock::Create(TheContext, "then", TheFunction);
+  BasicBlock *ElseBB = BasicBlock::Create(TheContext, "else");
+  BasicBlock *MergeBB = BasicBlock::Create(TheContext, "ifcont");
+
+  Builder.CreateCondBr(CondV, ThenBB, ElseBB);
+
+  // Emit then value.
+  Builder.SetInsertPoint(ThenBB);
+
+  Value *ThenV = Then->codegen();
+  if (!ThenV)
+    return nullptr;
+
+  Builder.CreateBr(MergeBB);
+  // Codegen of 'Then' can change the current block, update ThenBB for the PHI.
+  ThenBB = Builder.GetInsertBlock();
+
+  // Emit else block.
+  TheFunction->getBasicBlockList().push_back(ElseBB);
+  Builder.SetInsertPoint(ElseBB);
+
+  Value *ElseV = Else->codegen();
+  if (!ElseV)
+    return nullptr;
+
+  Builder.CreateBr(MergeBB);
+  // Codegen of 'Else' can change the current block, update ElseBB for the PHI.
+  ElseBB = Builder.GetInsertBlock();
+
+  // Emit merge block.
+  TheFunction->getBasicBlockList().push_back(MergeBB);
+  Builder.SetInsertPoint(MergeBB);
+  PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(TheContext), 2, "iftmp");
+
+  PN->addIncoming(ThenV, ThenBB);
+  PN->addIncoming(ElseV, ElseBB);
+  return PN;
+}
+
+// Output for-loop as:
+//   var = alloca double
+//   ...
+//   start = startexpr
+//   store start -> var
+//   goto loop
+// loop:
+//   ...
+//   bodyexpr
+//   ...
+// loopend:
+//   step = stepexpr
+//   endcond = endexpr
+//
+//   curvar = load var
+//   nextvar = curvar + step
+//   store nextvar -> var
+//   br endcond, loop, endloop
+// outloop:
+Value *ForExprAST::codegen() {
+  Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+  // Create an alloca for the variable in the entry block.
+  AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+
+  // Emit the start code first, without 'variable' in scope.
+  Value *StartVal = Start->codegen();
+  if (!StartVal)
+    return nullptr;
+
+  // Store the value into the alloca.
+  Builder.CreateStore(StartVal, Alloca);
+
+  // Make the new basic block for the loop header, inserting after current
+  // block.
+  BasicBlock *LoopBB = BasicBlock::Create(TheContext, "loop", TheFunction);
+
+  // Insert an explicit fall through from the current block to the LoopBB.
+  Builder.CreateBr(LoopBB);
+
+  // Start insertion in LoopBB.
+  Builder.SetInsertPoint(LoopBB);
+
+  // Within the loop, the variable is defined equal to the PHI node.  If it
+  // shadows an existing variable, we have to restore it, so save it now.
+  AllocaInst *OldVal = NamedValues[VarName];
+  NamedValues[VarName] = Alloca;
+
+  // Emit the body of the loop.  This, like any other expr, can change the
+  // current BB.  Note that we ignore the value computed by the body, but don't
+  // allow an error.
+  if (!Body->codegen())
+    return nullptr;
+
+  // Emit the step value.
+  Value *StepVal = nullptr;
+  if (Step) {
+    StepVal = Step->codegen();
+    if (!StepVal)
+      return nullptr;
+  } else {
+    // If not specified, use 1.0.
+    StepVal = ConstantFP::get(TheContext, APFloat(1.0));
+  }
+
+  // Compute the end condition.
+  Value *EndCond = End->codegen();
+  if (!EndCond)
+    return nullptr;
+
+  // Reload, increment, and restore the alloca.  This handles the case where
+  // the body of the loop mutates the variable.
+  Value *CurVar = Builder.CreateLoad(Alloca, VarName.c_str());
+  Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar");
+  Builder.CreateStore(NextVar, Alloca);
+
+  // Convert condition to a bool by comparing equal to 0.0.
+  EndCond = Builder.CreateFCmpONE(
+      EndCond, ConstantFP::get(TheContext, APFloat(0.0)), "loopcond");
+
+  // Create the "after loop" block and insert it.
+  BasicBlock *AfterBB =
+      BasicBlock::Create(TheContext, "afterloop", TheFunction);
+
+  // Insert the conditional branch into the end of LoopEndBB.
+  Builder.CreateCondBr(EndCond, LoopBB, AfterBB);
+
+  // Any new code will be inserted in AfterBB.
+  Builder.SetInsertPoint(AfterBB);
+
+  // Restore the unshadowed variable.
+  if (OldVal)
+    NamedValues[VarName] = OldVal;
+  else
+    NamedValues.erase(VarName);
+
+  // for expr always returns 0.0.
+  return Constant::getNullValue(Type::getDoubleTy(TheContext));
+}
+
+Value *VarExprAST::codegen() {
+  std::vector<AllocaInst *> OldBindings;
+
+  Function *TheFunction = Builder.GetInsertBlock()->getParent();
+
+  // Register all variables and emit their initializer.
+  for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
+    const std::string &VarName = VarNames[i].first;
+    ExprAST *Init = VarNames[i].second.get();
+
+    // Emit the initializer before adding the variable to scope, this prevents
+    // the initializer from referencing the variable itself, and permits stuff
+    // like this:
+    //  var a = 1 in
+    //    var a = a in ...   # refers to outer 'a'.
+    Value *InitVal;
+    if (Init) {
+      InitVal = Init->codegen();
+      if (!InitVal)
+        return nullptr;
+    } else { // If not specified, use 0.0.
+      InitVal = ConstantFP::get(TheContext, APFloat(0.0));
+    }
+
+    AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
+    Builder.CreateStore(InitVal, Alloca);
+
+    // Remember the old variable binding so that we can restore the binding when
+    // we unrecurse.
+    OldBindings.push_back(NamedValues[VarName]);
+
+    // Remember this binding.
+    NamedValues[VarName] = Alloca;
+  }
+
+  // Codegen the body, now that all vars are in scope.
+  Value *BodyVal = Body->codegen();
+  if (!BodyVal)
+    return nullptr;
+
+  // Pop all our variables from scope.
+  for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
+    NamedValues[VarNames[i].first] = OldBindings[i];
+
+  // Return the body computation.
+  return BodyVal;
+}
+
+Function *PrototypeAST::codegen() {
+  // Make the function type:  double(double,double) etc.
+  std::vector<Type *> Doubles(Args.size(), Type::getDoubleTy(TheContext));
+  FunctionType *FT =
+      FunctionType::get(Type::getDoubleTy(TheContext), Doubles, false);
+
+  Function *F =
+      Function::Create(FT, Function::ExternalLinkage, Name, TheModule.get());
+
+  // Set names for all arguments.
+  unsigned Idx = 0;
+  for (auto &Arg : F->args())
+    Arg.setName(Args[Idx++]);
+
+  return F;
+}
+
+const PrototypeAST& FunctionAST::getProto() const {
+  return *Proto;
+}
+
+const std::string& FunctionAST::getName() const {
+  return Proto->getName();
+}
+
+Function *FunctionAST::codegen() {
+  // Transfer ownership of the prototype to the FunctionProtos map, but keep a
+  // reference to it for use below.
+  auto &P = *Proto;
+  Function *TheFunction = getFunction(P.getName());
+  if (!TheFunction)
+    return nullptr;
+
+  // If this is an operator, install it.
+  if (P.isBinaryOp())
+    BinopPrecedence[P.getOperatorName()] = P.getBinaryPrecedence();
+
+  // Create a new basic block to start insertion into.
+  BasicBlock *BB = BasicBlock::Create(TheContext, "entry", TheFunction);
+  Builder.SetInsertPoint(BB);
+
+  // Record the function arguments in the NamedValues map.
+  NamedValues.clear();
+  for (auto &Arg : TheFunction->args()) {
+    // Create an alloca for this variable.
+    AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, Arg.getName());
+
+    // Store the initial value into the alloca.
+    Builder.CreateStore(&Arg, Alloca);
+
+    // Add arguments to variable symbol table.
+    NamedValues[Arg.getName()] = Alloca;
+  }
+
+  if (Value *RetVal = Body->codegen()) {
+    // Finish off the function.
+    Builder.CreateRet(RetVal);
+
+    // Validate the generated code, checking for consistency.
+    verifyFunction(*TheFunction);
+
+    return TheFunction;
+  }
+
+  // Error reading body, remove function.
+  TheFunction->eraseFromParent();
+
+  if (P.isBinaryOp())
+    BinopPrecedence.erase(Proto->getOperatorName());
+  return nullptr;
+}
+
+//===----------------------------------------------------------------------===//
+// Top-Level parsing and JIT Driver
+//===----------------------------------------------------------------------===//
+
+static void InitializeModule() {
+  // Open a new module.
+  TheModule = llvm::make_unique<Module>("my cool jit", TheContext);
+  TheModule->setDataLayout(TheJIT->getTargetMachine().createDataLayout());
+}
+
+std::unique_ptr<llvm::Module>
+irgenAndTakeOwnership(FunctionAST &FnAST, const std::string &Suffix) {
+  if (auto *F = FnAST.codegen()) {
+    F->setName(F->getName() + Suffix);
+    auto M = std::move(TheModule);
+    // Start a new module.
+    InitializeModule();
+    return M;
+  } else
+    report_fatal_error("Couldn't compile lazily JIT'd function");
+}
+
+static void HandleDefinition() {
+  if (auto FnAST = ParseDefinition()) {
+    FunctionProtos[FnAST->getProto().getName()] =
+      llvm::make_unique<PrototypeAST>(FnAST->getProto());
+    ExitOnErr(TheJIT->addFunctionAST(std::move(FnAST)));
+  } else {
+    // Skip token for error recovery.
+    getNextToken();
+  }
+}
+
+static void HandleExtern() {
+  if (auto ProtoAST = ParseExtern()) {
+    if (auto *FnIR = ProtoAST->codegen()) {
+      fprintf(stderr, "Read extern: ");
+      FnIR->dump();
+      FunctionProtos[ProtoAST->getName()] = std::move(ProtoAST);
+    }
+  } else {
+    // Skip token for error recovery.
+    getNextToken();
+  }
+}
+
+static void HandleTopLevelExpression() {
+  // Evaluate a top-level expression into an anonymous function.
+  if (auto FnAST = ParseTopLevelExpr()) {
+    FunctionProtos[FnAST->getName()] =
+      llvm::make_unique<PrototypeAST>(FnAST->getProto());
+    if (FnAST->codegen()) {
+      // JIT the module containing the anonymous expression, keeping a handle so
+      // we can free it later.
+      auto H = TheJIT->addModule(std::move(TheModule));
+      InitializeModule();
+
+      // Search the JIT for the __anon_expr symbol.
+      auto ExprSymbol = TheJIT->findSymbol("__anon_expr");
+      assert(ExprSymbol && "Function not found");
+
+      // Get the symbol's address and cast it to the right type (takes no
+      // arguments, returns a double) so we can call it as a native function.
+      ExitOnErr(TheJIT->executeRemoteExpr(ExprSymbol.getAddress()));
+
+      // Delete the anonymous expression module from the JIT.
+      TheJIT->removeModule(H);
+    }
+  } else {
+    // Skip token for error recovery.
+    getNextToken();
+  }
+}
+
+/// top ::= definition | external | expression | ';'
+static void MainLoop() {
+  while (true) {
+    fprintf(stderr, "ready> ");
+    switch (CurTok) {
+    case tok_eof:
+      return;
+    case ';': // ignore top-level semicolons.
+      getNextToken();
+      break;
+    case tok_def:
+      HandleDefinition();
+      break;
+    case tok_extern:
+      HandleExtern();
+      break;
+    default:
+      HandleTopLevelExpression();
+      break;
+    }
+  }
+}
+
+//===----------------------------------------------------------------------===//
+// "Library" functions that can be "extern'd" from user code.
+//===----------------------------------------------------------------------===//
+
+/// putchard - putchar that takes a double and returns 0.
+extern "C" double putchard(double X) {
+  fputc((char)X, stderr);
+  return 0;
+}
+
+/// printd - printf that takes a double prints it as "%f\n", returning 0.
+extern "C" double printd(double X) {
+  fprintf(stderr, "%f\n", X);
+  return 0;
+}
+
+//===----------------------------------------------------------------------===//
+// TCP / Connection setup code.
+//===----------------------------------------------------------------------===//
+
+std::unique_ptr<FDRPCChannel> connect() {
+  int sockfd = socket(PF_INET, SOCK_STREAM, 0);
+  hostent *server = gethostbyname(HostName.c_str());
+
+  if (!server) {
+    errs() << "Could not find host " << HostName << "\n";
+    exit(1);
+  }
+
+  sockaddr_in servAddr;
+  bzero(&servAddr, sizeof(servAddr));
+  servAddr.sin_family = PF_INET;
+  bcopy(server->h_addr, &servAddr.sin_addr.s_addr, server->h_length);
+  servAddr.sin_port = htons(Port);
+  if (connect(sockfd, reinterpret_cast<sockaddr*>(&servAddr),
+              sizeof(servAddr)) < 0) {
+    errs() << "Failure to connect.\n";
+    exit(1);
+  }
+
+  return llvm::make_unique<FDRPCChannel>(sockfd, sockfd);
+}
+
+//===----------------------------------------------------------------------===//
+// Main driver code.
+//===----------------------------------------------------------------------===//
+
+int main(int argc, char *argv[]) {
+  // Parse the command line options.
+  cl::ParseCommandLineOptions(argc, argv, "Building A JIT - Client.\n");
+
+  InitializeNativeTarget();
+  InitializeNativeTargetAsmPrinter();
+  InitializeNativeTargetAsmParser();
+
+  ExitOnErr.setBanner("Kaleidoscope: ");
+
+  // Install standard binary operators.
+  // 1 is lowest precedence.
+  BinopPrecedence['='] = 2;
+  BinopPrecedence['<'] = 10;
+  BinopPrecedence['+'] = 20;
+  BinopPrecedence['-'] = 20;
+  BinopPrecedence['*'] = 40; // highest.
+
+  auto TCPChannel = connect();
+  MyRemote Remote = ExitOnErr(MyRemote::Create(*TCPChannel));
+  TheJIT = llvm::make_unique<KaleidoscopeJIT>(Remote);
+
+  // Automatically inject a definition for 'printExprResult'.
+  FunctionProtos["printExprResult"] =
+    llvm::make_unique<PrototypeAST>("printExprResult",
+                                    std::vector<std::string>({"Val"}));
+
+  // Prime the first token.
+  fprintf(stderr, "ready> ");
+  getNextToken();
+
+  InitializeModule();
+
+  // Run the main "interpreter loop" now.
+  MainLoop();
+
+  // Delete the JIT before the Remote and Channel go out of scope, otherwise
+  // we'll crash in the JIT destructor when it tries to release remote
+  // resources over a channel that no longer exists.
+  TheJIT = nullptr;
+
+  // Send a terminate message to the remote to tell it to exit cleanly.
+  ExitOnErr(Remote.terminateSession());
+
+  return 0;
+}